Abstract
We herein present four cases of bone marrow (BM)-based B-cell neoplasms, which had non-IgM class M-proteins and carried the MYD88L265P mutation. Patients were in their fifties to eighties and were all male. Their presenting symptoms as well as routine laboratory test values were variable, and none had osteolytic bone lesions, renal insufficiency, or hypercalcemia or any signs or symptoms indicative of hyperviscosity. M-proteins in the serum of each case were IgG-κ and small amounts of IgM-κ in 1, IgG-κ in 2, and light chain λ only in 1, and Bence Jones protein was detected in the urine of 3. BM showed hypercellularity with the infiltration of 22.4-93.9% mature lymphocytes and cells with the plasmacytoid/plasma cell appearance were found in 2. Flow cytometry showed that neoplastic cells were uniformly positive for CD19, CD20, and CD22 and negative for CD5 and CD23. Increased numbers of mast cells were detected in 2 cases, while Dutcher bodies were observed in a few plasma cells in 1. We developed two polymerase chain reaction (PCR)-based tests to detect the MYD88L265P mutation and obtained PCR products indicative of the mutation in all four cases. Each patient was treated with rituximab alone or in combination with fludarabine or bendamustine, or bortezomib and dexamethasone. Although each case was formerly diagnosed with variable diseases, the presence of the MYD88L265P mutation indicated that all 4 cases were reliably classified into the category of lymphoplasmacytic lymphoma.
